Synthesis and structures of boron complexes of acyl hydroxy coumarins

Abstract

New boron chelates were synthesized by the reactions of 3 acetyl 4 hydroxycoumarin and 8 acyl 7 hydroxy 4 methylcoumarins with boron trifluoride etherate and hydroxybenzo dioxaborole. The structure of 3 acetyl 4 difluoroboryloxycoumarin containing an intramo lecular C=O...B coordination bond was established by X ray diffraction.

Aquatris[1-(2,4-dioxo-2H-1-benzopyran-3-ylidene)ethan-1-olato]ethanolgadolinium(III) ethanol monosolvate

“…For our part, we determined that the coordination ability of 3-acetyl-4-hydroxycoumarin towards lanthanides is related to the chelating character of the acetyl and hydroxyl groups, once the hydroxyl group has been deprotonated. The same behaviour has been reported for this ligand with a transition metal (Co II ; Bejaoui et al, 2018) and a data reports main-group element (B; Manaev et al, 2006). In the case of lanthanides, for which the coordination number is generally unpredictable, it is sometimes difficult to set up well-reproducible synthetic methods, especially when small coordinating molecules, such as water and alcohols, may be included in the coordination sphere.…”

Quantitative photooxidation of 4-hydroxy-3-pyrazolinylcoumarins to pyrazolyl derivatives

“…The precipitate was filtered off, dried and recrystallised from ethanol, 1, yellow crystals, yield 67%, mp 181-183°C. 1 …”

“…The precipitate was filtered off, dried and recrystallised from ethanol to give 2, yellow crystals, yield 56%, mp 149-151°C. 1 The rate of transformation also depends on the concentration of solution and the energy of illumination: under visible light, at a concentration of 10 -5 mol dm -3 , compound 1 undergoes 100% phototransformation for 1 h. At concentrations of 10 -3 mol dm -3 , the reaction was complete in 8 h: a solution of 1 (0.015 g, 0.036 mmol) in 30 ml of CCl 4 was illuminated by visible light for 8 h; after solvent evaporation, compound 2 was isolated: 0.0148 g (99% yield), mp 148-150°C. The illumination of 1 by 366 nm light at a low concentration provided its complete transformation into 2 for several minutes.…”

“…In a study of the synthesis and structural transformations of 4-hydroxycoumarin derivatives, [1][2][3][4] we found that 4-hydroxy-3-pyrazolinylcoumarin 1 was photooxidised to 4-hydroxy-3-pyrazolylcoumarin 2 under very mild conditions (Scheme 1). † We found that compound 1 (dissolved in CCl 4 ) changed its electronic absorption spectrum under illumination with visible light for 1 h (Figure 1).…”

Reactions of 2,3-dihydrofuro[3,2-c]coumarin-3-one with aromatic amines

“…5, 9 The resonance structures (Scheme 1) show a particular electron density distribution in its molecule, which determines the distinctive features of its reactivity.…”